JPS5896782A - Light-emitting element - Google Patents

Abstract

PURPOSE:To improve the contrast of the light-emitting part of the titled element by a method wherein a transparent film, which is thinner than an electrode in thickness, coated on a P-N junction and on the whole surface or on the part excluding the light-emitting part consisting of the P-N junction of the semiconductor substrate, whereon an electrode for application of a current is formed, thereby enabling to reduce scattering beams of light. CONSTITUTION:A P-N junction 3 is formed on the surface layer part of a semiconductor substrate 1, and one of annular electrode 2 is provided in such a manner that it comes in contact with the circumference of the P-N junction 3. Then a transparent film 5, which is thinner than the electrode 2 in thickness, is coated on the whole surface including electrode 2 and the junction 3, and other electrode 4 is installed on the entire back side of the substrate 1. According to this constitution, when the wavelength of an emitted light is considered to be lambda and the reflective index of the transparent film 5 is n, the thickness l of the film 5 is prescribed as l=(lambda/2n)(p+1/2). At this point, p is set at 0, 1, 2 and the like. Also, the film 5 may not be existed on the P-N junction 3, but anyhow the reflected beams of light are reduced, thereby enabling the light-emitting part to have a high contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light emitting element having a selective light emitting section, and aims to reduce scattered light and improve the contrast of the light emitting section.

Due to their high brightness and long life, light emitting diodes can be used not only as lamps but also as light sources for reading and writing information in information processing equipment. At this time, by making the light emitting part a specific shape and using a lens system to form an image, it is possible to obtain a light sporatra in a specific shape, making it possible to read and write information at that spot. . By the way, such a specific shape of the light emitting part can be achieved by selectively forming a pn junction which becomes the light emitting part on the light emitting diode substrate, which is required when used as a light source of information processing equipment. The conditions for this include high brightness and high contrast in the shape of the light spot. FIG. 1 shows an example of the configuration of a light source using GaAsP as a light emitting diode material. In FIG. 1, a is a thousand-sided view and b is a sectional view. GaAs
A P-type head area 3, which is a light emitting part, is selectively formed on a P substrate 1, and an electrode 2 at A constitutes an electrode for taking out the light to the outside. 4 is an n-side electrode. The P-shaped head region 3 indicated by diagonal lines is a light emitting shape, and this shape becomes a light emitting spot. However, in an optical system such as a lens system, various types of scattered light occur, and reflection occurs on the surface of the light emitting diode chip. In particular, since electrode 2 is made of Al, its reflectance is high;
In addition to the light emitted by the light emitting diode itself, reflected light from the chip surface occurs, resulting in a reduction in the contrast of the light emitting spot. This results in a decrease in resolution in information processing equipment, and improvements are required.

On the other hand, in order to eliminate the above-mentioned reflection on the chip surface and increase luminous efficiency, as shown in FIG. One coated with resin 12 is known. In this case, the light emitted from the light emitting diode chip 11 has a smaller relative refractive index at the interface with the resin 121, so if the angle of total reflection is small, more light is emitted inside the resin 12. Further, since the surface of the resin 12 is spherical, total reflection does not occur on the surface, so all the light inside the resin 12 is taken out to the outside, improving luminous efficiency. However, in this example, since the resin 12 has a lens shape, the resin lens cannot be used as a light source for information processing equipment that directly utilizes the shape of the light emitting part. To avoid this, conventional light sources for information processing equipment have used bare light-emitting diode chips, as shown in Figure 1, or those with transparent protective films formed on their surfaces, with low luminous contrast. .

The present invention solves these drawbacks by forming a transparent film on the surface of a light emitting diode chip, and by specifying the relationship between the thickness of this transparent film and the electrode, it improves the contrast as a light source and provides information. The present invention provides a light emitting element suitable as a light source for processing equipment. An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a diagram explaining the principle of the present invention, showing the optical paths of incident light and reflected light when a transparent film is coated on a semiconductor substrate. 1 is a semiconductor substrate, and 5 is a transparent film. The refractive index of the transparent film 5 is n1
If the angle of human radiation is θ, the angle of refraction is ψ, and the thickness of the transparent film is 4, then
The optical path difference Δ of the reflected light is expressed by the following equation with reference to FIG.

Δ=nPQR-PS n21 21sinθsin ψ ωSψ cosψ Substituting the relational expression of refraction sinθ-yl sinψ, Δ-2n l cosψ ・・・・・・・・・・・・
(1) When Δ is an appropriate value, the reflected lights interfere with each other, and when the wavelength of the light is λ, the reflected lights reach a minimum. If we consider that the main component of the incident light is in the vertical direction, then ψ-0, so (1).

From equation (2), when the thickness 4 of the transparent film 5 satisfies equation (3), the reflected light becomes minimum. That is, in the light emitting diode light source, by coating the semiconductor substrate 1 with the transparent film 5, reflected light can be reduced and contrast can be improved.

By the way, the coat of this transparent film 5 is the pn which is the light emitting part.
Although it is sufficient to apply the coating to areas other than the joints, the following 9th-order effect is produced by coating the light emitting areas as well. FIG. 4 shows that the light emitting part is also coated with the transparent film 5, but the optical path A of the light emitted from the light emitting part 3 on the substrate 1 would be such that if there was no transparent film 5, the incident angle of the person would be shallow. , total internal reflection as shown in B,
It is absorbed by the substrate 1 and does not go outside. but,
When the transparent film 5 is coated, the total reflection angle becomes small and the optical path A is guided into the transparent film 5. Thereafter, the light does not directly go outside due to total reflection, but when it propagates through the transparent film 5 and reaches the end, it is reflected by the Ag electrode 2 and emitted to the outside. Therefore, what is important here is the relationship between the thickness of the transparent film 5 and the A4 electrode 2,
If the Al electrode 2 is thin, the light emission effect described above will be extremely small, so the thickness of the electrode 2 needs to be thicker than the thickness of the transparent film 6. Therefore, the thickness of the transparent film 5 is (
3) It is set so that it satisfies the formula and is thicker than the thickness of the electrode 2 made of Ad or the like. The thickness of the electrode such as A/ is usually 2,000
0-3. For example, in the case of 6,600 red light emitting diodes, the thickness of the transparent film 5 is
3) Formula, J: ps3ooA, 99ooA is optimal.

There is also an example in which a transparent protective film is formed on the surface of the light emitting diode chip shown in Figure 1, but the thickness of the transparent protective film in this case is much thicker than the thickness of the electrode, which is 2,000 to 3,000λ. Therefore, the optical path A in FIG.
Such light is not extracted to the outside and has no effect of improving contrast.

5 and 6 are a sectional view and a plan view showing an embodiment in which the present invention is applied to a linear light source in which a plurality of light emitting diodes are arranged in a linear manner. As one application example of a light emitting diode light source, many light emitting parts are arranged on the same substrate and used as a numeric display element or a linear light source for an optical printer. At this time, since a plurality of light emitting parts are arranged adjacent to each other, light emission contrast deteriorates due to interference of light between adjacent light emitting parts. Furthermore, if the surface is coated with a transparent protective film that is thicker than the electrode, the light emitted will propagate in the surface direction through the film, resulting in an even greater reduction in contrast.

Therefore, the effects of the present invention are even more effective when a plurality of light emitting parts are provided. In FIGS. 5 and 6, the same parts as in FIG. 3 are given the same reference numerals.

As is clear from the figure, the electrode 2 is formed between each light emitting part 30, and since this thickness is thicker than the transparent film 5, the light emitted from the white of one light emitting part is reflected by the second part of the electrode, and the electrode 2 is thicker than the transparent film 5. While the intensity increases, the contrast does not deteriorate because the light from the adjacent light emitting section is blocked. As can be seen from the plan view of FIG. 6, the appropriate shape of the electrode is such that the electrode 2 covers the circumference of the light emitting part so that the light of the light emitting part itself can be contained within its own area.

As described above, the present invention provides selective [pn
In addition to forming an electrode for forming a junction and injecting current into this pn junction, a transparent film having a thickness thinner than the above electrode is provided on the entire surface of the semiconductor substrate including the pn junction and the electrode, or other than the light emitting part of the pn junction. It is possible to obtain an excellent light source with a large light emission output, low light scattering in areas other than the light emitting part, very good light emission contrast, high light emission efficiency, and no distortion of the light emission shape.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are a plan view and a cross-sectional view showing an example of a conventional light emitting diode light source, Figure 2 is a partial cross-sectional view showing another example of a conventional light emitting diode light source, and Figure 3 is a main view of the light source. 4 is a cross-sectional view showing an embodiment of the light-emitting device according to the present invention, and FIG. 6 is a cross-sectional view and a plan view of other embodiments of the light-emitting device according to the present invention. It is. 1... Semiconductor substrate, 2... Electrode, 3...
... pn junction, 4 ... n-type electrode, 5 ...
...transparent film. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (4)

[Claims] (1) A pn junction is selectively formed on the semiconductor substrate, and an electrode for injecting current into the pn junction is formed, and the above-mentioned A light emitting element characterized by forming a transparent film thinner than an electrode. (2) Claim 1, characterized in that the emission wavelength is set to λ, and the refractive index of the transparent film is set to n (provided that p-〇, 1, 2, etc.) The light emitting device described. (3) The light emitting device according to claim 1, which has one pn junction light emitting section on one semiconductor substrate. (4) The light emitting device according to claim 1, which has a plurality of pn junction light emitting parts on one semiconductor substrate.